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What did Rutherford discover about atoms?

• An atom is always negatively charged.

• An atom is mostly empty space, but has a dense positively charged center(nucleus).

• An atom is always positively charged.

• All particles will pass straight through gold foil with no change in path.

What is a positively charged particle?

• neutron

• electron

• proton

• atom

What is a particle with no charge?

• neutron

• electron

• proton

• atom

Rutherford's "gold-foil" experiment using alpha particle scattering concluded that

• the center of the atom is empty

• atomic mass is spread over the whole atom

• the center of the atom has a negative charge

• most of the atom is empty

This number is represented by the number of protons in the atom

• Atomic Mass
• Atomic Number
• Mass Number

How many subatomic particles are in Boron?

• 5 Protons

  4 Neutrons

  5 Electrons

• 5 Protons

  6 Neutrons

  5 Electrons

• 5 Protons

  5 Neutrons

  5 Electrons

• 5 Protons

  7 Neutrons

  5 Electrons

Answer explanation

Boron has the atomic mass of 10.810u meaning it has 6 neutrons (11u - 5p⁺ = 6n⁰); it has the atomic number 5 meaning it has 5 protons and 5 electrons.

(Remember to round the atomic mass!)

How many electrons (e^-) in Chlorine?

• 18

• 35

• 17

What is the mass number (atomic mass) of Titanium?

• 48

• 22

• 26

(challenge) An atom has 10 protons and 10 electrons. What happens to the charge if you add 1 more electron?

• It becomes a negative ion

• It becomes a positive ion

• nothing changes

• It becomes a different element

Challenge: what is the mass of an atom with 2 protons, 2 neutrons, and 2 electrons?

• mass = 2

• mass = 4

• mass = 6

• mass = 8